Selecting system



Patented Aug. 14, 1951 UNITED STATES PATENT OFFICE SELECTING SYSTEMMilton E. Mohr, New Providence, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication July 9, 1948, Serial No. 37,858

4 Claims. 1 1

vThis invention relates to improvements of selecting systems and morespecifically to improvements in selecting systems wherein a saturableinductance is used to increase the speed with which a circuit isselected.

One of the primary objects of the invention is to increase the speedwith which a circuit is selected for use from a plurality of lines,trunks, or other selectable circuits, while at the same time renderingall the other circuits of said lines, trunks or other selectablecircuits unselectable.

Asecond object of the invention is to utilize an inductance as a commonimpedance to a plurality of space discharge tubes, representingselectable circuits in such a manner that the inductance becomessaturated immediately after a tube ionizes, thus removing the inductiveimpedance of the saturated inductance and allowing the current in thespace discharge tube to increase rapidly.

Another object of the invention is to utilize a saturating inductance soas to increase the speed of operation of the selecting system. Afurtherobject is to use asaturating inductance in combination with aplurality of space discharge tubes such that when one tube begins toionize, the saturating reactance quickly acts to preclude any other tubefrom ionizing; each space discharge tube being individual to one vofaplurality of selectable circuits.

Another object of the invention is to improve the operation of selectingsystems generally.

An additional object is to make use of both the inductance and theresistance of the common inductive impedance to prevent other than onespace discharge tube from ionizing.

The invention consists of a selecting system of circuits, eachindividual circuit having a gas tube and a saturable inductanceimpedance common to all the gas tubes. A voltage is applied commonly toall the tubes causing one of them to ionize. The mathematical odds areextremely high that only one will ionize. When one tube ionizes, therising current will produce a drop in voltage across the commonimpedance and thus lower the voltage across the discharge gaps of theremaining tubes, eiectively preventing them from ionizing. The currentflowing through the tube that has ionized can be made to operate relaysin the circuit individual to the said ionized gas tube.

There are in theprior art one or more devices whereby a commonresistance or a common inductance hasv been used in series with a numberof gas tubes connected in parallel withrespect to each other. Thefunction of these devices has been to preclude more than one tube fromionizing.

In the instance of the common resistance, however, there was a chancethat more than one tube would ionize. To correct this deficiency acommon inductance with resistance was used. The probability of more thanone tube ionizing is considerably less than in the case where aresistance alone is used. But the use of the inductance presents aproblem, e. g. that the current was prevented, due to inductance in thecommon impedance, from rising rapidly to a sufficient value to operaterelays after the tube had ionized.

The objects of this invention are accomplished by causing the saturableinductance to become saturated immediately after the tube is ionized,thus allowing the current to increase to its full operating value muchmore quickly. Consequently, in applicants invention there is less timelag between the ionizing of the gas tube and the operation of the relaythan can be effected by use of a resistance or an ordinary inductance.The ionization of one tube, the transfer of its discharge, and theoperation of the associated magnet such as H0, III, or H2 may thereforebe made to occur more quickly. Although the time saved may not, at firstglance, seem consequential, it may amount to several tens ofmilliseconds, a time saving which may be of considerable consequence inthe telephone switching art wherein substantial expenditures may bejustified in order to save small amounts of time, it being noted in thepresent instance that the time saving is accomplished at substantiallyno increased cost, in fact, it may be accomplished at an actual decreaseof cost. The saturated inductance will inherently have a resistance ofsome value. This resistance is so calculated as to provide for a voltagedrop across said resistance after the tube has ionized and the elect ofthe inductance has become unimportant due to the leveling off of thecurrent. Such a voltage drop will lower the applied voltage across thedischarge gaps of the other gas tubes to a point suflicient to keep themfrom ionizing.

The aforementioned features and other features of the invention will bedescribed more fully in the following detailed speciiication.

This invention is applicable generally to selecting and connectingsystems but is disclosed in the drawing as used with a cross-bar type oftelephone system. For further explanation of a escales 3 cross-barsystem, reference is made to patent to Reynolds 2,021,329 of November19, 1935.

Referring to the drawing the subscribers lines 10 |02, etc., appear inthe vertical rows and the outgoing lines appear in the horizontal rows103, |015, |05, etc. Individual line raleys |09, |01, etc., and switchhold `magnets |08, |09, etc., represent the subscribers lines, andselect magnets H0, ||1, ||2, etc., represent the outgoing circuits. Eachoutgo-ing circuit is also represented by a space discharge tube H3, |14,H5, etc. Although several known gases are suitable, it has been foundthat argon filled tubes give satisfactory results. Ionization in thetube rst occurs across the two cathodes |22, 1|@ and then transfers tothe anode |29. The anodes of all the tubes are electrically connectedtogether through condensers |32, |33, 130, etc., which condensers areall connected to a common point. The left cathodes 122, 123, |20, etc.,of the tubes are all electrically connected to negative battery |28through armature of relay |26. The starting electrodes H6, IIS, ||9,etc., of the tubes are electrically connected through test conductors||1, |20, 12|, etc., respectively, through armatures of relays |35, |31,1&2, etc., respectivel to positive batteries 13 5, |33, 139, etc.,respectively. Each of the anodes |29, |39, |3|, etc., is connected toone of the select magnets 1|0, |11, |12, etc., respectively. Thesaturable inductance |21, which is a common impedance to all the tubes,is connected to negative battery |28. Resistances |50 and 15| are of avalue of approximately one megohm. Their purpose is to guard againstfalse operation of one or more oi the tubes which could be caused byleakage currents across the contacts of relay |255 when relay 126 isopen. The high resistances |59 and |51 provide a path for any suchleakage currents to flov,7 to ground Without developing appreciablevoltage at the tube terminals. Consequently, both the cathodes |22, |23,|24 and the anodes |29, |39., 13| of tubes H3, 1|l and H5 are held atground potential through high resistances and |50 respectively, prior tothe operation o f relay |26.

The operation of the invention will now be described in detail. Asubscriber of line picks up his receiver. This closes the circuitthrough lines 10| and the winding of relay 100, energizes relay 10G. Acircuit is thus completed from ground through the armature of relay |06,the winding of relay 126, to negative battery, and thence to ground,energizing relay |26, and closing the contacts of relay |26. This placespositive |09 volts on the anodes of the tubes through the left armatureof relay and the select magnets H0, 1|2, etc. 1t also places negative 59volts on the left cathodes of the tubes through the right-hand armatureof relay 126. Thus there isa difference of potential of 150 voltsbetween the anodes |29, |30, |3| and the cathodes |22, |23, |24 of thetube but this is insufficient to ionize the tubes. There is, however, apositive voltage of batteries 136, |38, |39, etc., applied tothe,starting electrodes H0, HS, ||9 of the tubes through conductors ||1,|20, |2I, etc., respectively. This creates a difference of potentialacross the cathodes and the starting electrodes of the tubes ofbatteries 136, |38, |39, etc., and battery |29. This difference ofpotential is sufficient to ionize the gas between the said cathodes andthe said starting electrodes. But only one of the tubes will ionize. Thetubes have inherently diiferent characteristics and one of them, tube113 for example, will begin to pass a little more space cur-l rent thanthe others. As this initial space current is of an increasing nature, acounter-electromagnetic force is induced in saturable coil inductance|21. This counter electromotive force reduces the applied Voltage acrossthe tubes and restrains the tubes, other than tube ||3, from ionizing.As long as the current through tube ||3 is increasing there will be acounterelectromagnetic force induced in saturable reactance |21 which,acting in cooperation with the resistance of said coil, will keep theother tubes from ionizing. Thesaturable core coil 121 is designed sothat immediately after the tube ||3 is drawing sufficient current sothat the tube can be said to be ionized, said suiiicient current hassaturated the saturable core coil and the current in the tube can thenrise to its full operating value unimpeded by an inductance in saturablecore coil |21. It is to be noted that the saturable core coil |21becomes saturated before the current in the tube has reached its fulloperating value. This feature allows a rapid rise of current in the tubeafter saturation of the saturable core coil 121 and a subsequent rapidoperation of relay H9. Before relay Hcan opcrate, however, theionization within the tube must transfer to anode |29. This transfer iseffected between cathode |22 and anode |29 after ionization has beenestablished between cathode |22 and starting electrode |19. After thetransfer is made a completed circuit exists .through positive battery|39, line 140, Winding of select magnet |12, anode 129, across the spacegap to cathode 122, line |25, through saturable core cc-il 121, tonegative battery |28. Select magnet 12 is operated almost immediatelysince satura-` ble core coil 121 is saturated and the inductance of saidcoil is ineffective to restrain the increase of current to operatingvalue.

The operation of select magnet prepares the horizontal row of cross-barcontacts, which appear in outgoing circuit |03, for further operation.Thereafter in any suitable manner a circuit is closed over conductor |4|for the operation of Ahold magnet |08. The operation of hold magnet |08closes the said cross-bar contacts and establishes a circuit from thesubscribers tele.- phone to the outgoing circuit |03. At this time,relay |35 which is under the control of the supervisory relay (notshown) operates to place ground potential upon the starting electrode land provides a holding circuit to ground for hold magnet |98. Since thevoltage of battery 128 is insufflcient to sustain an arc across the gap|22-I I3, said arc is extinguished. Relay |35 will remain energized aslong as the subscriber upon line |0| continues his call.

Referring again to hold magnet |03 which has just been energized overlead MI, it can be seen from the drawing that such energization of holdmagnet |09 opens lines I0| to deenergize relay |05 which in turn causesrelay |26 to deenergize. Deenergization of relay 126 opens the circuitfrom positive battery 139, armature ofrelay |25, line |40, selectmagnetv |0, anode |29, space gap to cathode |22, line |25, armature ofrelay |25, saturable core coil |21, to negative battery |28,deenergizing select magnet 10 and extinguishing tube |13. Y

If the subscriber upon line |02 should attempt to place acall, tube 113would not be affected, Relay |26 would be operated, in this case, fromthe ground on the armature of line `relay |01 in the manner previouslydescribed in connection with the line relay |06. However, relay |35 isoperated so long as the subscriber in line is still talking andtherefore the potential on electrode ||6 from line ||1 is ground fromthe front contact of and since the potential of cathode |22 is onlynegative 50 volts, there is insufcient voltage to ionize the |22||t` gapin tube H3. Since relays |31 and |42 are unoperated the potentials onelectrodes ||8 and ||9 of tubes ||4 and I5, respectively, is positiveVolts. The full starting gapuvoltages on tubes||4 and ||5 as describedheretofore in connection with tube I|3 is therefore 100 volts and one ofthese, ||5 for example, operates eventually connecting line |02 tooutgoing line I 04 in the manner herein described before.

When the subscriber of line |0| hangs up his receiver the supervisoryrelay (not shown)A operates to deenergize relay |35. Deenergization ofrelay |35 opens the holding circuit for relay |08 which then becomesdeenergized since there is a positive 50 volts on either side of thewinding of relay |08 and therefore no current can flow through saidwinding. In addition the deenergization of relay |35 places a negativebattery |36 on start electrode IIS to make tube H3 again ready foranother subscriber. The supervisory relay referred to above, its use ina complete system, and its mode of operation are well known to thoseskilled in the art; by way of one example out of many which might becited, reference is made to patent to Clark 1,844,147, dated February 9,1932, wherein the supervisory relay 202 controls a relay 204 whichcorresponds to and may be provided with contacts to perform thefunctions of any one of relays |35, |31, |42 of the present application.

In addition to the saturable core coil |21 acting to keep the tubes,other than tube I3, from ionizing, condensers |32, |33, |34, etc., alsoact to further decrease the voltage applied across anodes and cathodesof tubes other than tube I3. This is accomplished as follows: When tube||3 starts to ionize, current passes through select magnet ||0, causinga difference of potential across said select magnet. A current will nowfrom the positive side of said select magnet, along line |40, throughselect magnet III, and will charge condenser |33. This charging currentwill produce a voltage drop across select magnet and further decreasethe voltage applied to anode |30. Similar circuits and charging currentswill lower the anode voltage of tube |l5.

What is claimed is:

l. In an arrangement for interconnecting only one circuit of a rst groupof circuits to the same circuit of a second group, the combinationcomprising a plurality of gaseous discharge tubes each including a mainspace path and a control space path, a power source, an inductorincluding a winding magnetically coupled to a magnetizable coresaturable by current flow through said winding, said control space pathsbeing connected in a low impedance parallel connection with respect toone another and the combination thereof being connected in series withsaid power source and said saturable inductor when any one of vsaidfirst group of circuits requests to be connected to one of said secondgroup of circuits thereby applying an ionizing potential to said controlspace paths through said saturable inductor, a second power source, aplurality of actuating means individually connected to each of said mainspace paths through said second power source for interconnecting one ofsaid "6 second 'group of circuits associated therewith to one of saidrst group of circuits requesting an interconnection when said actuatingmeans is energized by ionization of its associated main space path, saidsaturable inductor preventing more than one of said control space pathsfrom being ionized at the same time by developing a potentialthereacross opposing the potential of said first power source incidentto the ionization of one of said control space paths thereby preventingan ionization breakdown potential from being applied to more than one ofsaid parallel connected control space paths, and said saturable inductorthereafter saturating so as to prevent a high value'surge potential frombeing developed thereacross due to ionization of one of said main spacepaths thereby diminishing the time interval during which the actuatingmeans associated with said ionized main space path is operated. A

2. In an arrangement employing a plurality of gaseous discharge deviceswherein only one of said devices is to be fully ionized within a shorttime interval to the exclusion of the other of said devices, each ofsaid devices comprising a main space path and a control space path, aplurality of impedance elements individually connected in series with adifferent main space path in the power supply circuit therefor, saidcontrol space paths being connected into a low impedance parallelconnection, an inductor including a winding magnetically coupled to amagnetizable core saturable by current ilow through said winding andbeing connected in series with said parallel connected control spacepaths in the power supply circuit therefor, and said saturable inductorpreventing more than one of said control space paths from being ionizedat the same time by developing a potential thereacross opposing thepotential applied to said parallel connected control space paths by thepower supply circuit therefor incident to the ionization of one of saidcontrol space paths thereby preventing an ionization breakdown potentialfrom being applied to more than one of said parallel connected controlspace paths, and said saturable inductor thereafter saturating so as toprevent a high value surge potential from being developed thereacrossdue to ionization transfer to one of said main space paths therebydiminishing the time interval during which the impedance elementassociated with said ionized main space path attains peak potentialthereacross.

3. In an arrangement employing a plurality of gaseous discharge deviceswherein only one of said devices is to be fully ionized within a shorttime interval and each of said devices includes an auxiliary space pathand a control space path, said auxiliary space path having a lodimpedance element individually connected to the power supply circuittherefor, and said control space path being connected in a low impedanceparallel connection, the improvement which comprises an inductorsaturable by current now therethrough being connected in series with apower supply circuit for said parallel connected control space pathsthereby preventing more than one of said control space paths from beingionized at the same time by developing a potential thereacross opposingthe potential applied to said parallel connected control space paths bythe power supply circuit therefor incident to the ionization of one ofsaid control space paths so as to prevent an ionization breakdownpotential from being paths being connected, into a low impedanceVparallel connection, an inductor saturable by current flow therethroughin series with said parallel connected gaseous paths, a power supplysource being connected to said inductor-gaseous space pathsubcornbination so thatA the ionizing potential for said space paths isapplied through said saturable inductor whereby a potential opposing thepotential of said power supply source is developed acrosssaid` saturableinductor 'incident to the ionization of one of said gaseous space pathsthereby preventing more than one of said space paths from ionizing andsaid saturable inductor thereaftersaturating due to the magnitude ofcurrent ow therethrough so. as to attain peak current ow therethroughyin a short time interval after lock-out.

MILTON E. MOHR.

REFERENCES CITED The Vfollowing references are of recordrin the le ofthis patent:

vUNITED STATES PATENTS Number Name Date 1,943,524 Godsey Jan. 16, 19342,320,076 Hall s May 25,1943 2,326,551 Mohr Aug. 10, 1943

